[SPIR-V] Implement SPV_KHR_float_controls2 (#146941)
Implementation of
[SPV_KHR_float_controls2](https://github.khronos.org/SPIRV-Registry/extensions/KHR/SPV_KHR_float_controls2.html)
extension, and corresponding tests.
Some of the tests make use of `!spirv.ExecutionMode` LLVM named
metadata. This is because some SPIR-V instructions don't have a direct
equivalent in LLVM IR, so the SPIR-V Target uses different LLVM named
metadata to convey the necessary information. Below, you will find an
example from one of the newly added tests:
```
!spirv.ExecutionMode = !{!19, !20, !21, !22, !23, !24, !25, !26, !27}
!19 = !{ptr @k_float_controls_float, i32 6028, float poison, i32 131079}
!20 = !{ptr @k_float_controls_all, i32 6028, float poison, i32 131079}
!21 = !{ptr @k_float_controls_float, i32 31}
!22 = !{ptr @k_float_controls_all, i32 31}
!23 = !{ptr @k_float_controls_float, i32 4461, i32 32}
!24 = !{ptr @k_float_controls_all, i32 4461, i32 16}
!25 = !{ptr @k_float_controls_all, i32 4461, i32 32}
!26 = !{ptr @k_float_controls_all, i32 4461, i32 64}
!27 = !{ptr @k_float_controls_all, i32 4461, i32 128}
```
`!spirv.ExecutionMode` contains a list of metadata nodes, and each of
them specifies the required operands for expressing a particular
`OpExecutionMode` instruction in SPIR-V. For example, `!19 = !{ptr
@k_float_controls_float, i32 6028, float poison, i32 131079}` will be
lowered to `OpExecutionMode [[k_float_controls_float_ID]]
FPFastMathDefault [[float_type_ID]] 131079`.
---------
Co-authored-by: Dmitry Sidorov <dmitry.sidorov@intel.com>
